Modified 5-HT3A receptor function by co-expression of alternatively spliced human 5-HT3A receptor isoforms

Naunyn Schmiedebergs Arch Pharmacol. 2000 Nov;362(4-5):392-401. doi: 10.1007/s002100000342.


Serotonin (5-HT) exerts fast excitatory responses by activation of 5-HT3 receptors, irrespective of whether they are homomerically composed of 5-HT3A subunits or heteromerically assembled of 5-HT3A and 5-HT3B subunits. Here we describe a short, truncated (h5-HT3AT) and a long (h5-HT3AL) splice variant of the human 5-HT3A (hS-HT3A) receptor subunit. The deduced protein of the short isoform consists of 238 amino acids (aa) with a single transmembrane domain (M1). Compared to the known 5-HT3A receptor, the long isoform contains 32 additional aa in the extracellular loop between M2 and M3. Both splice variants are co-expressed together with the 5-HT3A subunit in the amygdala and hippocampus, whereas in the placenta only the short variant is co-expressed. Both splice variants, when expressed in transfected human embryonic kidney (HEK) 293 cells, are not able to form functional homomeric receptors, but modify 5-HT response at heteromeric h5-HT3A receptors. Co-expression of the short variant considerably decelerates the desensitization of the 5-HT3 receptor; thus, heteromeric assemblies of h5-HT3A and the h5-HT3AT subunit exhibit 5-HT-induced cation fluxes which are much larger than those of homomeric hS-HT3A receptors. In contrast, heteromeric complexes containing the h5-HT3AL subunit display reduced cation fluxes. In conclusion, the splice variants increase the functional diversity of 5-HT3 receptors.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Alternative Splicing*
  • Amino Acid Sequence
  • Cloning, Molecular
  • Humans
  • Molecular Sequence Data
  • Protein Isoforms / analysis
  • Protein Isoforms / physiology
  • Radioligand Assay
  • Receptors, Serotonin / chemistry
  • Receptors, Serotonin / genetics
  • Receptors, Serotonin / physiology*
  • Receptors, Serotonin, 5-HT3
  • Tumor Cells, Cultured


  • Protein Isoforms
  • Receptors, Serotonin
  • Receptors, Serotonin, 5-HT3